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std::set<Key,Compare,Allocator>:: set

From cppreference.net

C++
Containers library
std::set
Member functions
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
(1)
set ( ) ;
(until C++11)
set ( ) : set ( Compare ( ) ) { }
(since C++11)
(constexpr since C++26)
explicit set ( const Compare & comp,
const Allocator & alloc = Allocator ( ) ) ;
(2) (constexpr since C++26)
explicit set ( const Allocator & alloc ) ;
(3) (since C++11)
(constexpr since C++26)
template < class InputIt >

set ( InputIt first, InputIt last,
const Compare & comp = Compare ( ) ,

const Allocator & alloc = Allocator ( ) ) ;
(4) (constexpr since C++26)
template < class InputIt >

set ( InputIt first, InputIt last,
const Allocator & alloc )

: set ( first, last, Compare ( ) , alloc ) { }
(5) (since C++14)
(constexpr since C++26)
set ( const set & other ) ;
(6) (constexpr since C++26)
set ( const set & other, const Allocator & alloc ) ;
(7) (since C++11)
(constexpr since C++26)
set ( set && other ) ;
(8) (since C++11)
(constexpr since C++26)
set ( set && other, const Allocator & alloc ) ;
(9) (since C++11)
(constexpr since C++26)
set ( std:: initializer_list < value_type > init,

const Compare & comp = Compare ( ) ,

const Allocator & alloc = Allocator ( ) ) ;
(10) (since C++11)
(constexpr since C++26)
set ( std:: initializer_list < value_type > init,

const Allocator & alloc )

: set ( init, Compare ( ) , alloc ) { }
(11) (since C++14)
(constexpr since C++26)
template < container-compatible-range < value_type > R >

set ( std:: from_range_t , R && rg,
const Compare & comp = Compare ( ) ,

const Allocator & alloc = Allocator ( ) ) ;
(12) (since C++23)
(constexpr since C++26)
template < container-compatible-range < value_type > R >

set ( std:: from_range_t , R && rg,
const Allocator & alloc )

: set ( std:: from_range , std:: forward < R > ( rg ) , Compare ( ) , alloc ) { }
(13) (since C++23)
(constexpr since C++26)

Constructs new container from a variety of data sources and optionally using user supplied allocator alloc or comparison function object comp .

1-3) Constructs an empty container.
4,5) Constructs the container with the contents of the range [ first , last ) .
If [ first , last ) is not a valid range , the behavior is undefined.
6,7) Constructs the container with the copy of the contents of other .

If alloc is not provided, allocator is obtained by calling std:: allocator_traits < allocator_type > ::
select_on_container_copy_construction ( other. get_allocator ( ) ) .

(since C++11)

During class template argument deduction , only the first argument contributes to the deduction of the container's Allocator template parameter.

(since C++23)
8,9) Constructs the container with the contents of other using move semantics. If alloc is not provided, allocator is obtained by move-construction from the allocator belonging to other .

During class template argument deduction , only the first argument contributes to the deduction of the container's Allocator template parameter.

(since C++23)
10,11) Constructs the container with the contents of the initializer list init .
12,13) Constructs the container with the contents of rg .

Contents

Parameters

alloc - allocator to use for all memory allocations of this container
comp - comparison function object to use for all comparisons of keys
first, last - the pair of iterators defining the source range of elements to copy
other - another container to be used as source to initialize the elements of the container with
init - initializer list to initialize the elements of the container with
rg - a container compatible range , that is, an input_range whose elements are convertible to value_type
Type requirements
-
InputIt must meet the requirements of LegacyInputIterator .
-
Compare must meet the requirements of Compare .
-
Allocator must meet the requirements of Allocator .

Complexity

1-3) Constant.
4,5) N·log(N) where N is std:: distance ( first, last ) in general, linear in N if [ first , last ) is already sorted by value_comp ( ) .
6,7) Linear in size of other .
8,9) Constant. If alloc is given and alloc ! = other. get_allocator ( ) , then linear.
10,11) N·log(N) where N is init. size ( ) in general, linear in N if init is already sorted by value_comp ( ) .
12,13) N·log(N) where N is ranges:: distance ( rg ) in general, linear in N if rg is already sorted by value_comp ( ) .

Exceptions

Calls to Allocator::allocate may throw.

Notes

After container move construction (overload ( 8,9 ) ), references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in * this . The current standard makes this guarantee via the blanket statement in [container.reqmts]/67 , and a more direct guarantee is under consideration via LWG issue 2321 .

If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844 ).

Although not formally required until C++23, some implementations has already put the template parameter Allocator into non-deduced contexts in earlier modes.

Feature-test macro Value Std Feature
__cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion; overloads ( 12,13 )

Example

Run this code 
#include <cmath>
#include <iostream>
#include <set>
#include <string>
struct Point { double x, y; };
struct PointCmp
{
    bool operator()(const Point& lhs, const Point& rhs) const
    {
        return std::hypot(lhs.x, lhs.y) < std::hypot(rhs.x, rhs.y);
    }
};
std::ostream& operator<<(std::ostream& os, Point pt)
{
    return os << '(' << pt.x << ',' << pt.x << ')';
}
void println(auto rem, const auto& seq)
{
    std::cout << rem << '{';
    for (auto n{seq.size()}; const auto& elm : seq)
        std::cout << elm << (--n ? ", " : "");
    std::cout << "}\n";
}
int main()
{
    // (1) Default constructor
    std::set<std::string> a;
    a.insert("horse");
    a.insert("cat");
    a.insert("dog");
    println("1) a: ", a);
    // (4) Range constructor
    std::set<std::string> b(a.find("dog"), a.end());
    println("2) b: ", b);
    // (6) Copy constructor
    std::set<std::string> c(a);
    c.insert("another horse");
    println("3) c: ", c);
    // (8) Move constructor
    std::set<std::string> d(std::move(a));
    println("4) d: ", d);
    println("5) a: ", a);
    // (10) Initializer list constructor
    std::set<std::string> e{"one", "two", "three", "five", "eight"};
    println("6) e: ", e);
    // Custom comparison
    std::set<Point, PointCmp> f = {{2, 5}, {3, 4}, {1, 1}};
    f.insert({1, -1}); // This fails because the magnitude of (1,-1) equals (1,1)
    println("7) f: ", f);
    // (12) Range constructor
    const auto w = {"Eurybia", "Theia", "Rhea", "Aura", "Mnemosyne", "Mnemosyne"};
#if __cpp_lib_containers_ranges
    std::set<std::string> g(std::from_range, w); // overload (12)
#else
    std::set<std::string> g(w.begin(), w.end()); // fallback to (4)
#endif
    println("8) g: ", g);
}

Possible output: 

1) a: {cat, dog, horse}
2) b: {dog, horse}
3) c: {another horse, cat, dog, horse}
4) d: {cat, dog, horse}
5) a: {}
6) e: {eight, five, one, three, two}
7) f: {(1,1), (3,3), (2,2)}
8) g: {Aura, Eurybia, Mnemosyne, Rhea, Theia}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2076 C++11 overload ( 4 ) conditionally required Key to be CopyInsertable into * this not required
LWG 2193 C++11 the default constructor was explicit made non-explicit

See also

assigns values to the container
(public member function)